1. Field of the Invention
The present invention relates to an active matrix display device having light-emitting elements arranged in a matrix which are driven by driving means provided for each of the light-emitting elements. The present invention relates more particularly to a technique for providing improved yield of an active matrix display device.
2. Description of the Related Art
An organic EL display device using organic electroluminescence elements (hereinafter referred to as organic EL elements) has been known as a self-luminous active matrix display device. That is, an organic EL display has organic EL elements arranged in a matrix and driving means for each of the organic EL elements. An organic EL element is a current light-emitting element which has an organic substance layer between its anode and cathode electrodes. The organic substance layer includes a hole transporting layer and light-emitting layer stacked one upon another. The light-emitting layer includes an organic substance. Therefore, an organic EL display provides a color gradation by controlling the current level flowing through each of the organic EL elements with the driving means.
FIG. 17 is a plan view illustrating a reference example of wiring structure of an organic EL display 110.
FIG. 18 is a sectional view of the organic EL display 110 shown in FIG. 17 in the row direction (horizontal direction in FIG. 17).
As illustrated in FIG. 17, the organic EL display 110 has organic EL elements 120 arranged in a matrix of m rows by n columns (2 rows by 3 columns in FIG. 17 for simplification).
Here, the organic EL display 110 has TFTs (thin film transistors) 130 (TFT 130a and TFT 130b), capacitor (capacitive element) 140 and other components on a substrate 111 (refer to FIG. 18). On the other hand, each of the TFTs 130 includes, as illustrated in FIG. 18, a gate insulating film 132, a-Si (amorphous silicon) layer 133 and protective film 134 stacked on a gate electrode 131. The TFT 130 also includes a source electrode 135 on the left side of the a-Si layer 133 and a drain electrode 136 on the right side thereof. It should be noted that an n+ a-Si layer 137 is provided to ensure excellent ohmic contact between the a-Si layer 133 and source electrode 135 or drain electrode 136.
On the other hand, a signal line 151 is disposed on the gate insulating film 132. The signal line 151 is one of the drive wirings adapted to drive the organic EL element 120. An insulating film 160 is stacked above the TFT 130 and signal line 151. The insulating film 160 includes an insulating protective film 161 and insulating planarizing film 162. The insulating planarizing film 162 has a flat surface free from irregularities. It should be noted that the drive wirings include not only the signal line 151 but also a scan line 152 and power line 153 as illustrated in FIG. 17. These wirings are disposed in the insulating film 160.
Still further, the organic EL element 120 is disposed on the insulating planarizing film 162 illustrated in FIG. 18. The same element 120 has an organic substance layer 123 between an anode electrode 121 and cathode electrode 122. The anode electrode 121 is connected to the TFT 130 via a connection hole (not shown) formed in the insulating film 160. It should be noted that the organic substance layer 123 includes an organic substance adapted to emit light as a result of the recombination of injected electrons and holes.
Still further, the cathode electrode 122 is a transparent electrode. Therefore, light emitted by the organic substance layer 123 is extracted from the center portion of an opening regulating insulating film 124 surrounding the anode electrode 121. That is, the organic EL display 110 is a top emission display designed to extract light from the side opposite to the substrate 111.
Incidentally, the top emission organic EL display uses a transparent electrode as the cathode electrode 122 as described above so that light emitted by the organic substance layer 123 can be extracted. However, a conductive material having a high transmittance is high in resistance. On the other hand, a metal having a high reflectance, for example, is used for the anode electrode on the side of the substrate 111. Therefore, an auxiliary wiring 154 is disposed around the anode electrode 121 and connected to the cathode electrode 122 to reduce the resistance of the same electrode 122.
The auxiliary wiring 154 is provided on the same layer as the anode electrode 121 as illustrated in FIG. 18. The same wiring 154 overlaps the signal line 151 one above the other. The same line 151 is disposed for each row of the organic EL elements 120 arranged in a matrix. As illustrated in FIG. 17, the auxiliary wiring 154 also overlaps the scan and power lines 152 and 153 one above the other. The scan and power lines 152 and 153 are each disposed for each row of the organic EL elements 120. The auxiliary wiring 154 is insulated from the signal, scan and power lines 151, 152 and 153 by the insulating film (refer to FIG. 18). Further, although the signal line overlaps each of the scan and power lines 152 and 153 one above the other at the intersection, the signal line is insulated from the scan and power lines 152 and 153 by the insulating film 160.
However, the entry of a foreign object, for example, in the manufacturing process may lead to a short circuit, resulting in a lower yield. That is, improper etching in the course of fabricating the TFTs 130 may cause an intralayer short circuit, or dust or other impurity may cause an interlayer short circuit. This leads to a point or line defect in which all the organic EL elements 120 in one entire row or column are faulty, thus resulting in a poor yield. A possible solution to this would be to prevent the auxiliary wiring 154 from overlapping the signal line 151 or other lines by reducing the width of the same wiring 154 or reducing the area over which the same wiring 154 is disposed. This solution, however, leads to a voltage drop across the auxiliary wiring 154, resulting in crosstalk. Further, the signal lines 151 arranged as illustrated in FIG. 17 intersect the scan and power lines 152 and 153.
For this reason, a matrix-wired substrate is known which permits repair of a short circuit. That is, this technique forms a pair of openings in advance in an interlayer insulating film so that the intersection is sandwiched between gate and drain lines. The drain line crosses over the gate line. The interlayer insulating film covers the drain line. The drain line is exposed in the openings. If a short circuit is detected at the intersection between the two lines due to a defect of the interlayer insulating film in the inspection process, the interlayer insulating film is destroyed on the inside (short-circuited side) of each of the pair of openings sandwiching the short-circuited area, after which the drain line beneath the interlayer insulating film is cut off. Then, a bypass line is formed so as to bypass the short-circuited area via the pair of openings, thus rejoin the cut segments of the drain line (refer, for example, to Japanese Patent Laid-Open No. 2000-241833, hereinafter referred to as Patent Document 1).